Follow BI

Sometimes I wake up in the middle of the night and can't move — here's why

Every few months
I have a terrifying experience in the middle of the night.

I wake up but can't move, except for my eyes, which dart
frantically underneath fluttering, heavy lids. I feel a heavy
presence on top of my chest, squeezing the air from my lungs and
throat. Then a shadowy, cloaked figure starts looming just within
the corners of vision.

Ad

I'm not dreaming. And no matter how many times it happens, the
panic sets in. As a kid, I thought the devil had paid a visit to
my bedroom.

Now I know these symptom stem from a strange sleep phenomenon
called sleep paralysis. While various social and psychological
factors can influence the prevalence of sleep paralysis, a
2011
paper combined 35 studies with more than 36,000 participants
total. The authors found that 7.6% of the general population
experiences sleep paralysis, rising to 28.3% in high-risk groups,
like students who have a disrupted sleep pattern. And in people
with mental disorders, like anxiety and depression, 31.9%
experienced episodes.

"When you're experiencing sleep paralysis, you become conscious,"
Daniel Denis, a PhD candidate in cognitive neuroscience and
researcher at the
Sleep Paralysis Project, tells Business Insider. "The idea is
that your mind wakes up but your body doesn't."

Why you can't move

Sleep has
three or four stages of non-REM (rapid eye movement) sleep
and one REM state. While people can dream in any stage, REM is
the most closely associated with vivid dreams, the type that seem
real.

The
brain also stays active during REM - "almost comparable to
during the day," Denis explains. People naturally become
paralyzed during REM, probably to prevent themselves from acting
out their dreams, a process known as REM atonia.

Many who wake up during this state simply open their eyes and
quickly begin to move around. But those suffering from sleep
paralysis experience "a sort of failure of the molecular clock,"
as Denis puts it. For whatever reason, REM atonia continues after
you've waken up. Most episodes last a few seconds to a minute,
but in much rarer cases, people can require 10 to
15 minutes before they fully regain motion.

About that shadowy friend of mine - researchers don't have the
best explanations for it. To start, I could be experiencing my
brain's interpretation of myself. The parietal lobes may be
monitoring the neurons in my brain telling my limbs to move,
according to a study from UC San Diego, published in the journal
Medical Hypotheses. Since they can't, the brain hallucinates the
intended movement.

Denis explains that the "intruder" might also be due to an
over-active amygdala, a part of the brain responsible for fear
(among other things). "You wake up with your amygdala screaming,
'There's a threat!'" he explains. "So your brain has to invent
something to fix the paradox of the amygdala being active for no
reason." While the amygdala remains active during REM sleep,
total paralysis right after awakening can send it into overdrive.

The experiences

One of the first in-depth studies on sleep
paralysis in 1999 defines the three main categories of sleep
paralysis hallucinations as the "incubus," the "intruder" and
"unusual bodily experiences."

In the first case, people feel an intense pressure on their
chests, inducing the feeling that they can't breathe.

As the authors note, sleep paralysis affects only the "perception
of respiration." Breathing is reflex-based, so nothing truly
separates these poor few from the oxygen they desperately need.
It just feels that way because they're afraid.

"When you're in REM, your breathing is very shallow and your
airways become quite constricted, so it would be difficult to
breath anyway," Denis explains. "But when you become conscious of
that, it can be terrifying."

People experiencing the second category, the "intruder," can feel
a "sensed presence, fear, and auditory and visual
hallucinations," the researchers note. Essentially, your mind
invents a vision to solve some sort of paradox in the brain that
occurs during sleep paralysis. The authors describe it as a
"hypervigilant state of the midbrain," which can make people
highly aware of even the smallest stimuli and "biased toward cues
for threat or danger." That's why a small sound can seem
horrifying to someone experiencing sleep paralysis.

The intruder and the incubus go hand-in-hand. Both symptoms
typically involve the threat-activated
systems in the amygdala, as mentioned earlier. Some people
even relate the "intruder" and the incubus, reporting that they
feel someone strangling or suffocating them, Denis says. But the
third type of sleep paralysis hallucination, the "unusual bodily
experiences" are the least common.

When people experience "unusual bodily experiences," they often
feel like they're having an out-of-body experience, levitating or
flying around the room, as the 1999 study explains. This third
type appears to be associated with REM stages where the
brainstem, cerebellar, and cortical vestibular centers are
activated, according to a 2013
study of 133 patients with panic disorder.

The pons, which inhibits movement during sleep, falls into that
area, Denis notes. "You feel like you're moving when you're not
because the area of the brain that coordinates that is
overactive," he says.

Myths and folklore

Cultural beliefs also strongly influence these hallucinations and
experiences, leading to the creation of folklore and myth, which
can blur fact with fiction. The "Old Hag," for
example, is the primary interpretation of sleep paralysis in
Newfoundland. And similar fantastical stories exist about the
Boto, a pink river dolphin in the Amazon Basin that transforms at
night into a lustful prowler, explains "The Devil in the Room," a
documentary that explores the paranormal and mythical aspects of
sleep paralysis.

Take a look at Henry Fuseli's 1781 oil painting, "The Nightmare,"
shown below, thought to be one of the clearest artistic
interpretations of sleep paralysis.

caption

Henry Fuseli's "The Nightmare," 1781.

Personally, my over-active amygdala conjures images of the devil
- unsurprising considering I live in a majorly Christian nation
and grew up mildly Catholic. From his research, Denis says that
"modern Western culture" tends to see burglars, rapists, and
aliens.

Prevention

While sleep paralysis can be hereditary, it can happen to anyone.
Factors like lack of
sleep, sleep disturbances, jet lag, and shift work can
increase someone's likelihood of experiencing it, and certain
groups, like African-Americans,
can also experience it more commonly. Sleep-paralysis episodes
have been linked to hypertension, seizures, and narcolepsy, a
sleep disorder where people lose their ability to regulate sleep
cycles and can fall asleep at random and unexpected moments.

While stress, anxiety, and depression often trigger the episodes,
we can't exactly control these factors. So beyond trying to
reduce stress and getting plenty of sleep, how can you prevent
the terrifying onset of sleep paralysis?

Avoiding sleeping on your back could help. Research has
shown that people that experience sleep-paralysis episodes
are three to four times more likely to occur in people who sleep
in the supine position. Some people even use nightwear that makes
lying on their back uncomfortable, according to Denis.

But if you do wake and find yourself unable to move, focus all
your energy on wiggling a toe or finger. "So long as you can move
one muscle, that breaks the paralysis," Denis advises.